1. Field of the Invention
The presently disclosed invention generally relates to improvements on a submersible electrical power generating plant. More specifically, the presently disclosed invention is primarily intended for providing an improved electrical power generating plant that is able to generate electricity from the kinetic energy contained in steady ocean currents.
2. Description of the Prior Art
Perhaps the most frightening aspect about the approaching energy crisis is that so few are aware of the seriousness of the problem and the devastating impact that the worsening shortages of oil and natural gas will have upon our industrialized society, upon our nation, and upon our lives. The decline in the production of both world oil and North American natural gas—combined with catastrophic global warming—have created an urgent need to switch from fossil fuels to those energy sources that are sustainable and non-polluting. Oceans' currents flow at all depths, with the strongest usually occurring in the upper layer, which is shallow compared to the depth of the oceans. The main cause of surface currents in the open ocean is the action of the wind on the sea surface.
Winds of high constancy, blowing over great stretches of an ocean, have the greatest effect on producing current. It is for this reason that the northwest and southeast trade winds of the two hemispheres are the mainsprings of the ocean's surface current circulation. In the Atlantic and Pacific oceans the two trade winds drive an immense body of water westwards over a width of some 50 degrees of latitude, broken only by the narrow belt of the east-going Equatorial Counter-current, which is found a few degrees north of the equator in both of these oceans. A similar westward flow of water occurs in the South Indian Ocean, driven by the southeast trade wind. These westward surface currents produce giant eddies that are centered in latitudes of approximately 30 degrees N. and S. that rotate clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere. Currents of over 3.5 mph are confined to very restricted regions. They have been recorded in the equatorial regions of the oceans, and in the warm currents flowing to higher latitudes in the western sides of the oceans. Ocean Passages of the World (published by the Hydrographic Department of the British Admiralty, 1950), lists 14 currents that exceed 3 knots (3.45 mph), a few of which are in the open ocean.
The Gulf Stream and the Kuroshio are the only two currents that the book lists having velocities above 3 knots that flow throughout the year. The book states the strongest currents recorded for the Gulf Stream and the Kuroshio in nautical miles per day. These speeds are equivalent to 156.5 statute miles per day (6.52 mph) for the Gulf Stream, and 133 statute miles per day (6.375 mph) for the Kuroshio. Because these speeds were determined by how far the current carried floating objects in 24 hours, they do not reflect the maximum current speeds at specific times or places. Both the Gulf Stream and the Kuroshio are currents that are driven by the Coriolis force that is produced by the earth's eastward rotation acting upon the ocean currents produced by the trade winds. Because these currents are caused by the earth's eastward rotation, they will continue flowing through the Straits of Florida for as long as our planet continues to turn on its axis.
In addition to producing the Coriolis Effect that produces the oceans' gyres, another consequence of the earth's eastward rotation is that the center of each of those gyres is offset toward the western edge of the ocean basin that confines it. Because the volume of water flowing toward the poles along the narrower western sides of the gyres is the same as that circulating back toward the Equator down the much broader eastern expanses, the constricted western currents are forced to flow much faster than their eastern counterparts. This is what makes the Gulf Stream and the Kuroshio such powerful currents. Because the Gulf Stream's current is relatively consistent, well-placed turbines powered by that current should generate usable electricity virtually one hundred percent of the time.
The Gulf Stream starts roughly where the Gulf of Mexico narrows to form a channel between Cuba and the Florida Keys. From there the current flows northeast through the Straits of Florida between the mainland and the Bahamas, flowing at a substantial speed for some 400 miles. It hits peak velocity off Miami, where the Gulf Stream is about 45 miles wide and 1,500 feet deep. There the current has reached a speed of as much as 7.75 mph in its narrow central axis. Although the peak current velocity of the Gulf Stream may at times exceed 7 mph in its narrow axis off of Miami, the most likely velocities for those turbines placed in its central axis would most probably be between 4.75 and 6 mph.
As previously stated, the Kuroshio's maximum flow rate is only slightly slower than that of the Gulf Stream. Although turbines designed for the Gulf Stream can also generate low-cost electricity from the Kuroshio, they would probably not operate at quite the same high capacity factors in that current as they would in the Gulf Stream. This is because the velocity of the Kuroshio fluctuates more due to both seasonal and tidal effects, flowing slower in the fall and with rising tides. The current has two stable path patterns south of Honshu, the largest island of Japan. It has a straight path that flows eastward, after passing the tip of the Kii Peninsula, and it has a large meandering path that flows around a large coldwater mass that can form to the southwest of that peninsula Either pattern can persist for periods ranging from several months to several years. Because of the Kuroshio's changing paths and the extreme water depths in the area, there is only one location where the turbines can consistently produce power. That is just south of the Izu Peninsula and Sagami Bay, where both current paths pass over the Izu-Ogasawara Ridge, where the Pacific Plate subducts under the Philippine Sea Plate.
Other possible sites for submersible power plants include the East Australian Coast current, which flows at a top rate of 110.47 statute miles per day (4.6 mph), and the Agulhas current off the tip of South Africa, which flows at a top rate of 139.2 statute miles per day (5.8 mph). Oceanographic current data will suggest other potential sites. Tidal currents are of interest—not because a tethered submersible power generator would be well suited for harvesting their kinetic energy—but because they also involve the generation of electricity underwater, the transmission of that power to shore, and because serious money is being invested in their development, even though their capacity factors are very low. The tides are the periodic motion of the water caused by the differences in the gravitational attractive forces of the moon and the sun acting on all the different parts of the rotating Earth. As the tides rise and fall, periodic horizontal movements of water accompany them: the tidal currents. The variations in the speed of the tidal currents from place to place are not consistent with the range of the tides and, depending on the shape of the coastline; they can even be the reverse.
Although there is presently no interest in producing more power from a tide's changing water level, there is a growing interest in the tidal currents. As with all turbine power plants, the ability to produce electricity depends on the efficiency of the design and on the speed and steadiness of the fluid driving it. Although the usable current velocities that drive the tidal turbines can be about the same as those that would drive turbines placed in the Gulf Stream, the tidal currents oscillate and can produce power only between the high and low tides. The strengths of the tidal currents will also vary greatly depending the phases of the moon and whether the current is being produced by a spring tide or by a neap tide. As a result of the tidal current's oscillations and variations, the capacity factors for these tidal systems would almost certainly be less than 10 percent of the system's theoretical generating capacities. Because the capacity factors for the turbines operating in the Gulf Stream would be seven to ten times those of the tidal-powered turbines, they would produce seven to ten times as much power, and—unlike that wildly oscillating power produced by the tidal turbines—that power would be almost as steady as that power produced by many fossil-fuel plants. Although there will be some changes in the current's velocity, caused by the moon's tidal effects and the steadiness of the trade winds, the only renewable energy source that would have higher capacity factors than those of well-placed turbines in the Gulf Stream would be the conventional hydroelectric power plants that have sufficient water in their reservoirs.
Well-placed turbines in the Gulf Stream will spin whether or not there is any demand for their electricity. Because they would operate best under steady loads and because their operating costs would be virtually zero that power they produce that is in excess of that required by the grid can be used to produce energy in other forms. This can include the charging of batteries to power vehicles and the production of hydrogen. Common energy efficiencies for the electrolysis of water are at about 65%. However, by using catalysts in the water electrolyte, efficiencies of 80% to 85% are possible. The amount of hydrogen that can be produced by this method is directly proportional to the amount of electricity used. Instead of adding more gas-fired generating capacity to handle the periods of peak demand, we should strive to generate more than enough power from the water turbines' free energy to cover the peak loads and then add additional loads to fully utilize the surplus generating capacity during periods of low demand from the grid.
In this way, not only can these submersible turbines eliminate the need for fossil fuels to produce electricity, they can produce electricity for recharging the batteries of “plug-in” hybrid vehicles and hydrogen to power fuel-cell vehicles. Producing hydrogen by electrolysis can eliminate the need for a hydrogen transportation infrastructure because the hydrogen can be produced from water at local fueling stations during off-peak periods. Every kilowatt-hour of electricity that is generated by water, wind, and other renewable-energy sources can replace the same unit of electricity that is presently being generated by burning fossil fuels. Based on a study in the UK, that determined the carbon dioxide emission of their fossil-fuel plants, each of the submersible electrical power generating plants, having a design capacity of 1200 kilowatts and operating with a 90 percent capacity factor, would reduce the carbon dioxide emissions by roughly 8,100 US tons per year from that produced by the fossil-fuel plants producing the same amount of electricity.
Water has much more mass than air and would be moving more slowly. A cubic unit of water weighs about 854 times the same cubic unit of air at sea level. The amount of kinetic energy that passes through a turbine can be calculated using the formula:KE=½×M×V2 M=mass V=velocityThe mass is the weight of the fluid that passes through the turbine's rotor per second. This can be obtained by calculating the blades' sweep area and multiplying that quantity by the distance the fluid travels in one second. This volume is then multiplied by the weight of the fluid per cubic unit to get the mass. Because the mass passing through the blades in one second is a factor of the current's velocity, the power produced by the current does not increase by the square of its velocity, but by its cube. Therefore, the equation for the kinetic energy passing through a turbine can also be written:(KE=½×A×D×V3 A=area swept D=density/cu.m. V=velocity)
Rotor Diameters to Generate 600 Kilowatts of Electricityin Currents of Different Velocities in MPHAssuming 45%Efficiencycurrentrotorvelocitydiameter7.034.16.538.16.043.05.549.05.056.54.566.24.079.03.596.53.0110.0
To increase the RPM and reduce the torque to manageable levels, the power from the hubs is transferred in either three or four stages to the shaft powering the generator. The first stage consists of a strongly built planetary gear system. A second planetary gear system is either attached to a third planetary gear system or to helical gears, depending on the revolutions and torque of the shaft coming from the first stage. The last stage consists of helical gears—and, depending on the sizing of the gears in the first two or three stages, a fourth stage of helical gears could be required to increase the generators' shaft speeds to the 1,200 RPM required by the 6-pole generators and the 1,800 RPM required by the 4-pole generators to produce electricity that is compatible with the 60 Hz current used in the US. The technology to generate electric power from the kinetic energy contained in the moving water can be virtually identical to that used by the wind-power industry.
Wind turbines that generate electric power usually have two or three long, narrow rotor blades. The have these long blades—not because they can capture the most energy from the wind—but because the blades must be able to survive violent wind conditions. A wind turbine with many blades or very wide blades (turbines with a solid rotor) would be subject to extremely large forces when the wind blows at hurricane velocities because the energy increases with the cube of its velocity. To limit the impact from these extreme conditions, the manufacturers of the wind machines prefer that their turbines have only two or three long narrow rotor blades that can be feathered and locked. Because most of the force driving the Gulf Stream portion of the North Atlantic's gyre is produced by the steady eastward rotation of our planet, the current's speeds tend to remain within a narrow range. Very rarely do they exceed 7 mph or drop below 4 mph in the current's central axis off South Florida. Because the water would be nearly a thousand times denser than the air and would be flowing at a much more constant velocity, instead of their rotors having just two or three narrow blades to absorb the kinetic energy from a small percentage of the fluid passing through the sweep area, they can have more or wider blades.
All generators produce heat. The electric current flowing through the conductors, both the stator and rotor, produces heat because of resistance. In addition, heat is generated in the steel of the rotor armature core by the changing of magnetic lines. Although the amount of heat from all the losses in large generators is only about one percent of the output, it can be numerically great. For example, a pair of generators producing a total of 1,200 kW might have a loss of 12 kW—equivalent to 40,973 Btu per hour. Unlike the wind turbines that can operate on hot summer days, the water turbines would operate in water having temperatures of about 70° Fahrenheit. However, because plastics do not have the same ability to transfer heat as do the metal housings used on the wind turbines, and because there will be no outside source of air for cooling, some type of external cooling system will be required to dissipate the heat produced by the generators and gearboxes.
A major concern for any tethered submersible power plant is the downward vector force that is produced by the horizontal-drag force acting through the downward-angled anchor line. That downward force will equal the horizontal drag, multiplied by the tangent of the anchor line's downward angle where it attaches to the generating plant. If a tethered generating power plant is to maintain a uniform depth, any changes in the downward vector forces must be balanced be equal opposing forces. If the increasing downward vector force is not equalized, the downward vector forces will pull the submersible power plant down to that depth where the angle of the anchor chains' pull would be reduced sufficiently that the tangent of the attachment angle will be reduced enough that the resulting downward-vectored forces will again balance the reduced lifting forces. The forces would again be in equilibrium and the unit would remain at that depth as long as there were no further changes in the horizontal drag. Because the downward forces increase at an increasing rate as the angle of the downward pull increases, the angle of the anchor chain where it attaches to the unit should be kept reasonably small. That angle should also be kept small because the forces pulling on the anchor line will increase with the reciprocal of the cosine (the secant) of the angle—and as that angle increases, increasing the pull on the anchor chain, the anchor's holding ability is decreasing.
Most of the prior art for generating electricity from ocean currents can be grouped into a few categories. There are the water wheels and rotating canisters that are mounted on vertical shafts that have V-shaped, cupped or articulated buckets, fins, or flippers to reduce the resistance to the water when the periphery of the wheels are moving toward the current. U.S. patents in this group include U.S. Pat. No. 3,973,864 issued to Atherton, U.S. Pat. No. 4,038,821 issued to Black, U.S. Pat. No. 4,134,710 issued to Atherton, U.S. Pat. No. 4,551,066 issued to Frisz, U.S. Pat. No. 4,748,808 issued to Hill, U.S. Pat. No. 4,818,888 issued to Lenoir, and U.S. Pat. No. 6,006,518 issued to Geary. There are patents for devices having vertical turbines that are mounted on horizontal shafts that do not use shrouds or other devices that surround the rotors. These patents include U.S. Pat. No. 4,023,041 issued to Chappell, U.S. Pat. No. 4,137,005 issued to Comstock and U.S. Pat. No. 5,440,176 issued to Haining. Then there are more U.S. patents that use turbines mounted on horizontal shafts in which the rotors are enclosed in shrouds, flarings, hollow tubes, Venturi-shaped tubes, or have funnel-shaped intakes for the purpose of increasing the water velocity through the turbine. Examples of these include U.S. Pat. No. 3,980,894 issued to Vary, U.S. Pat. No. 3,986,787 issued to Mouton, U.S. Pat. No. 4,095,918 issued to Mouton, U.S. Pat. No. 4,163,904 issued to Skendrovic, U.S. Pat. No. 4,205,943 issued to Vauthier, U.S. Pat. No. 4,306,137 issued to Wracsaricht, U.S. Pat. No. 4,335,319 issued to Mattersheimer, U.S. Pat. No. 4,520,273 issued to Rowe, U.S. Pat. No. 6,064,123 issued to Gislason. Counter-rotating impellers are used in U.S. Pat. No. 4,203,702 issued to Williamson. The blades on these devices overlap and there are V-shaped diverters located ahead of the turbines force the fluid to the outside of the turbines.
All the inventions mentioned above are devices that are mounted on underwater structures or are suspended from barges, pontoons, or platforms on pylons at the surface. The problem with mounting the generating devices on platforms is that the strongest currents are located near the surface where the depths are usually greater than 1,200 feet and mounting the generating devices high above the ocean floor on giant structures would be extremely costly. Because the turbines would be producing their drag forces far from the ocean floor, they would produce huge tipping moments that would equal the horizontal drag of the structure, multiplied by height of those drag forces above the ocean floor. If the structures had shorter towers, the submersible power plants would be much more difficult to install and service and the turbines would be beneath the stronger current flow. The problem with suspending the turbines from barges or pontoons is that they would interfere with ship traffic, be vulnerable to violent storms, and be unsightly.
Among the patented inventions to generate electricity from ocean currents, there are tethered devices that rely on hydrofoils and/or ballast tanks to provide lifting forces to keep the devices at the desired depths. U.S. Pat. No. 6,091,161 issued to Delhsen uses variable-pitch rotor blades to limit the drag force. Although this patent may have things in common with the presently disclosed invention in that they are both tethered and have counter-rotating, rear-facing turbines, the inventions are very different. The Delhsen's submersible underwater generating device would have little or no stability because, with the buoyancy tank being between the heavy elements and not above them, its center of buoyancy is not above the center of gravity.
Also the lifting force provided by the hydrofoil that joins the nacelles is at the same level as the heavy elements, further adding to a lack of stability. The upward canted hydrofoil wing tips that supposedly provide roll stability would have little or no effect unless the hitch points to the two anchor lines were lower. Because the anchor lines attach directly ahead of the center of drag, the canted wing tips would have little effect on stability. The resistance to roll is further decreased in the Delhsen invention by the anchor line's attachment point being at the same height as the center of buoyancy rather than below it. With the attachment point located at the center of buoyancy, if the device should have positive buoyancy, the canted wing tips would decrease stability. The placement of the stabilizer fin forward of the hydrofoil makes no sense. With the anchor attachment points being behind this “stabilizing fin,” the fin would make the device more unstable. The device uses two anchors, each connected to capstans that are located at the front of each nacelle to adjust the anchor chains to eliminate yaw.
The hydrofoil between the nacelles contains separate ballast tank compartments that are capable of being filled with fluid or purged to control buoyancy and the shift the center of buoyancy. The nacelles also contain buoyancy tanks that can be independently filled or purged to compensate for roll of the device. The Delhsen invention utilizes a computer system to balance those forces produced by the hydrofoil, buoyancy and drag to allow the device to seek that current that will allow for an even production of electric power. The drag force on the rotors is controlled by adjusting the pitch of the rotor blades so that the device seeks an initial equilibrium velocity of water current that will allow the tethered device to stay within a chosen predetermined depth range. A problem with this approach is that, although the purpose of the generator is to capture kinetic energy to maximize power output, it controls the depth by reducing that output.
U.S. Pat. No. 6,109,863 issued to Milliken is another tethered unit that consists of a buoyant device that contains two counter-rotating water wheels or turbines that are mounted side-by-side on vertical shafts. The vanes of the turbine have sub-vanes that open when the large vanes are moving toward the current to allow the water to pass through them. Although these are counter-rotating turbines are side-by-side, because they are mounted on vertical shafts, their counter rotation has no effect on the device's stability. In this and all other devices that use turbines mounted on vertical shafts—not only are the areas for capturing the energy of the moving fluid small in proportion to the frontal area of the device, they waste additional energy because—even though the fins on the reverse side of the vertical turbine may fold or open to allow water to have much less resistance as they rotate toward the front of the turbine—they still produce some drag that must be subtracted from the power produced by that side of the turbine that is being pushed by the kinetic energy of the flowing water.
The inefficiencies of all these vertical shafted turbines can be compared to using paddle wheels for propelling boats rather than modern propellers, except they would be worse because the top blades of a boat's paddle wheel meets far less resistance when moving forward through the air than would those blades of a vertical-shafted water turbine blades moving against the much denser water. Also the invention has no means of balancing changing downward vector forces that would result from changes in drag, caused by changes in either the current velocity or changes in the generator loads acting on the downward angled anchor line.
U.S. Pat. No. 4,219,303 issued to Mouton is a tethered unit with a pair of axle-less, counter-rotating, co-axial turbine wheels having ring rims that bear against friction drive wheels which turn one or more electrical generators that are contained in water-tight rooms within the wall of a nozzle or shroud that surround the periphery of the turbines. To increase the velocity of the water through the turbines, the device has an opening nozzle in the front that directs the water into a narrowing vena contracta, through the two counter-rotating, co-axial turbines and then on to an expanding shroud downstream that is for the purpose of increasing the water's velocity. This device depends on buoyancy and a weight on the bottom to maintain the proper depth. Many devices use vertical turbines mounted radially on horizontal shafts that are enclosed in shrouds, hollow tubes, Venturi-shaped tubes, or have funnel-shaped intakes to increase the fluid velocity through the turbines. Although it is possible for the velocity of a fluid passing through a vertical turbine's sweep area to be increased somewhat by using these devices, tests have shown that the turbines' input can be increased at much lower cost by simply increasing the rotors' diameters. Shrouds and Venturi-shaped tubes are not used on commercial wind-powered turbines because they do not increase the velocities enough to justify their cost. Instead of using such devices, the manufacturers of the wind machines increase the diameters of the turbine rotors.
A key consideration when designing a tethered submersible generator is that of stability. A fully submerged object that is floating freely in a liquid will float with its center of buoyancy (the center of gravity of the fluid that the object is displacing) directly above the objects center of gravity. The prior art does not show tethered submersible electrical power plants that utilized this principal of physics, except for U.S. Pat. No. 6,531,788 ('788 patent), which is issued to the author and discloses a first submersible generating plant for producing electricity from ocean currents, as briefly described hereinafter.
The '788 patent teaches an apparatus comprising two counter-rotating, rear-facing turbines with a plurality of rotor blades extending radially outward from two separate horizontal axis that convey the kinetic energy from the two side-by-side turbine rotors through separate gearboxes to separate generators that are housed in two watertight nacelles that are located sufficiently far apart to provide clearance for the turbine rotors. The two generators and their gearboxes serve as ballast and are located below a streamlined buoyancy tank that extends fore and aft above and between them. A leverage system having no moving parts adjusts lifting forces to balance changing downward vector forces that result from changes in drag acting on the downward angled anchor line.
Although previous inventions may also generate electric power with low operating costs, none can produce as much power at such low cost per kilowatt-hour as the currently disclosed invention because of its highly efficient energy-collecting design and its extremely low maintenance requirements. Thus, it is a principal object of the current invention to provide a submersible electrical power generating plant that is capable of being free of service or replacement for many years. It is a further object of the current invention to provide a stable submersible electrical power generating plant that has its center of buoyancy located above its center of gravity. It is a still further object of the current invention to provide a submersible electrical power generating plant that has an adjustable center of gravity. It is a further object of the current invention to provide a submersible electrical power generating plant that is capable of generating electrical power from low speed current flow when equipped with turbines, generators, and gearing are properly sized for the slow current.
Still further, it is an object of the current invention to provide a non-polluting means of producing steady, low-cost electric power than can be used to cover both base and peak load requirements. It is a further object of the current invention to provide a tethered submersible electrical power generating plant that will remain within any pre-set range of depths without requiring a line being attached to a weight on the ocean floor. It is a further object of the current invention to provide a submersible electrical power generating plant designed to facilitate the efficient simultaneous submersions of many of the submersible electric power generating plants that have been assembled into strings while floating on the surface by throwing an electric switch. It is a further object of the current invention to provide a submersible electrical power generating plant with a simple and efficient method for bringing an individual submersible power generating plant to the surface and of removing the ballast water. It is a further object of the present invention to provide a method for simultaneously raising a group of many power plants to the surface without being disconnected from the electricity collecting table.
It is a further object of the current invention to provide a submersible electrical power generating plant having low parasite drag (that drag that does not contribute to the capturing of energy or providing lift) and which a high percentage of the horizontal drag forces are from that kinetic energy that is actually converted into electricity. It is a further object of the current invention to provide a submersible electrical power generating plant that is made of carbon fiber composites and other plastics to minimize displacement and eliminate corrosion. It is a further object of the current invention to provide a submersible electrical power generating plant that has improved directional stability. It is a further object of the current invention to utilize the same changes in the current's kinetic energy that changes the downward vector forces to adjust the lifting forces to balance those downward forces.
It is a further object of the current invention to utilize those unchanging lifting forces produced by displacement to support the unchanging weight of the submersible electrical power generating plant, and to utilize those changing lifting forces produced by the hydrofoils to balance the changing downward vector forces. It is a further object of the current invention to provide a submersible electrical power generating plant capable of using hydrostatic pressures to control the hydrodynamic lifting forces to accurately and reliably control operating depths. It is a further object of the current invention to provide a means for bringing the submersible electrical generating structures quickly to the surface and to purge the buoyancy tank of ballast water with pressurized air.
Other objects of the current invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or apparent from, the following description and the accompanying drawing figures.